California’s Largest Living Roof Crowns Green Museum

On Sept.27, San Francisco will celebrate the opening of what is being called the greenest museum in the world – the new California Academy of Sciences. Slated for LEED Platinum certification, one of the most spectacular features of the museum is the 2.5-acre Living Roof.

Designed by world-renowned living architecture and ecological habitat firm Rana Creek in collaboration with the Renzo Piano Building Workshop and SWA Landscape Architecture, the Academy’s Living Roof is the largest in California and the most technically advanced in the world. Using the most breakthrough designs and green building practices the Living Roof integrates ecology with architecture to blend seamlessly with the museum and surrounding areas.

 Architect Renzo Piano’s concept was to create the impression that the park had been lifted up and the museum placed underneath it. Working on the design and logistics with Paul Kephart’s Rana Creek team, the result is a 2.5-acre, 2.6 million pound roof with 1.7 million native plants arranged on seven rolling hills that mimic the surrounding Golden Gate Park landscape.

Green Roof Benefits

The Living Roof on the California Academy of Sciences serves many environmental benefits. The Living Roof will:

• \Mitigate storm water runoff – by absorbing up to 3.6 million gallons of water per year (about 98 percent of all storm water), the roof will prevent runoff from carrying pollutants into San Francisco’s water system.
• Insulate and cool buildings – the heavy layers of soil and vegetation will keep interior temperatures around 10 degrees cooler than a standard roof.
• Reduce the urban heat island effect – the evaporation and transpiration activity will keep the Living Roof surface an average 40 degrees cooler than a standard roof, which helps to mitigate the problem that cities collect heat over dense building masses.
• Natural ventilation – Boasting the steepest slopes of any living roof in the world, these were designed specifically to draw cool air into the open piazza at the center of the building, naturally ventilating the surrounding exhibit spaces.

Plant Selection

For five years, the Rana Creek team worked closely with the California Academy of Science’s botany team led by Frank Almeda and the SWA Landscape Architecture team to determine the native plant species that would thrive on the roof without fertilizer or irrigation. The group chose nine species – four perennials and five annual wildflowers that attract a host of other wildlife including bees, birds and the endangered Bay Checkerspot and San Bruno Elfin butterflies.

The Solution

The slopes on the Living Roof’s rolling hills accommodate the Academy’s domed planetarium, rainforest, and aquarium exhibits. Rana Creek developed a patented solution called the BioTray to address the dual challenge they faced: how to create the Living Roof without using toxic plastics or petrochemicals, and how to prevent the plants from slipping off the rolling hills. These modular 17-inch square and three-inch deep biodegradable trays made out of coconut husk and tree sap serve as planters as well as roof tiles. The porous BioTray works with the building’s structure and natural botanical processes in a unique interpretation of nature. The plants’ roots spread between the BioTrays to form a locked, woven network of vegetation and a very stable base even on sloping surfaces.

“We are thrilled to have been involved in the creation of the most sustainable museum in the world, and to see the roof develop into a thriving ecosystem in full bloom in just a few months,” said Paul Kephart, executive director at Rana Creek. “We look forward to continuing to work with the Academy to promote their mission to explore, explain and protect the natural world.”